According to this somewhat unnerving article in the UK's daily Telegraph, the UK military is already examining the military affects of a break-up of the Eurozone - http://www.telegraph.co.uk/news/uknews/defence/8957513/Eurozone-crisis-poses-military-risk-warns-defence-chief-General-Sir-David-Richards.html. The article also states that European economies could contract by up to eight percent in that scenario. Here is also one particularly unnerving quote from the article:
"The military planning work has come to light after The Daily Telegraph disclosed last month that British embassies in the eurozone have been told to prepare emergency plans for the demise of the euro and the possible civil disorder that could follow."
Whilst not given to hyperbole, one can only note that this is scary stuff.